ICAMS / Interdisciplinary Centre for Advanced Materials Simulation
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Determination of dislocation density from atomistic data

Date: 11.10.2009
Place: ECI Conference on Nanomechanical Testing 2009, Barga, Italy

Jun Hua
Alexander Hartmaier

Large-scale molecular dynamics simulations have been widely used to investigate the mechanical behavior of materials. But complex datasets generated during the atomistic simulations involving the positions of many million atoms make quantitative data analysis quite a challenge. This paper presents a novel method to determine dislocations in the crystal and also quantifies the corresponding Burgers vectors. This is achieved by combining geometrical methods to determine the atoms lying in the dislocations cores, like for example the common neighbor analysis or the bond angle analysis, with the slip vector analysis. The first methods are used to filter out the atoms lying in undisturbed regions of the crystal; the latter method yields the relative slip of the remaining atoms and thus indicates the Burgers vector of those atoms lying in the dislocation cores. The validity of the method is demonstrated on single edge dislocations in relatively small samples. Large-scale atomistic simulations of nanoindentation reveal the full potential of the slip vector analysis. It is found that the Burgers vector of dislocations can be reconstructed from the slip vectors. Based on this data, the density of geometrically necessary dislocations (GND) is evaluated by the summation of the normalized slip vectors of the atoms sitting at the dislocation lines. The GND density is investigated as a function of the deformed volume, the indentation depth and the indenter size. This method can be expected to provide valuable input for multi-scale modeling.

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